Process of flameproofing and rot-proofing cellulosic materials by applying acidic solutions of antimony, zirconium and titanium and neutralizing with ammonia gas



PROCESS OF FLAWEPROOFING AND ROT-PROOF- ING CELLULOSIC lVlATERIALS BY APPLYING ACIDIC SOLUTIONS (3F ANTIMONY, ZIRCO- NIUM AND TITANIUM AND NEUTRALIZING W H H AMltdGNIA GAS Wesley W. Riches, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application December 7, 1953, Serial No. 396,780

6 Claims. (Cl. 8116) This invention pertains to the treatment of textile materials. It deals in particular with an improved method of neutralizing the acid residues left after cellulosic textile materials have been treated with acidic aqueous solutions such as those of titanium and antimony used in flame-proofing textiles.

Many Water insoluble basic metallic compounds may be precipitated within the fine structures of textiles, and cellulosic materials in general especially paper for various purposes other than flame-proofing such as imparting mildew and rot resistance, resistance to photodegradation, modifying the dyeing properties, and changing the strength and other mechanical properties. In these treatments it is desirable to deposit the impregnating substances cleanly and efficiently.

It has long been recognized that a serious fire hazard exists in cellulosic textile materials. This fire hazard represents not only a potential loss of materials, but constitutes a major cause for injury and loss of human life. The danger to persons is especially evident wherever inflammable textile materials are used in the construction of tents, clothing, draperies and paper decorations. To combat this hazard numerous flameproofing treatments have been developed. Among the many proposed methods of imparting flame resistance or flame retardation to cellulosic materials, those which currently seem to be most successful involve impregnating the inflammable material with an acidic aqueous solution of antimony and titanium and fixing these elements within the fabric by such means as heating, aging, and neutralization of the acid. Some of these solutions and the methods employed in applying them are described in some detail in U. S. Patents 2,570,566 and 2,607,729 and also in the pending application by W. L. Dills, Serial #245,089 now U. S. Patent 2,668,784. As these references indicate, the neutralization step is desirable both to render the treatment permanent and to remove the residual acid which would otherwise harm the fabric. The alkaline agents which have been used to neutralize these acids include aqueous solutions of sodium carbonate, sodium hydroxide, and ammonium hydroxide. In practice, considerable care has to be exercised during the neutralization step in order to avoid the precipitation of dusty residues on the fabric. Although this dust can usually be laundered away, it is not always possible to produce a clean fabric. Furthermore, the loss of any such dust represents inefficiency in the application of the flame-proofing chemical-s.

It is, therefore, an object of this invention to provide certain improvements in the process of impregnating textiles and other cellulosics with the aforementioned agents. Another object is to simplify the operation with respect to the number of solutions which must be handled. Still other objects relate to the improvement of the appearance of the finished products and to the increased efiiciency of application of flame-proofing and other chemicals.

These objects and others are attained by my invention which broadly comprises treating or wetting an, absorbent organic material especially cellulosic compositions with States Patent ice an aqueous acidic solution of at least one polyvalent metal whose oxide and hydroxide are substantially insoluble in water, exposing the treated material to ammonia gas thereby effecting neutralization of at least a portion of the acid remaining in said treated material, and recovering an improved product impregnated with a basic or oxygenated compound of said metal such as the oxide, hydroxide, hydrous oxide or other water insoluble hydroxy or oxy salt.

This invention, when adapted to process for imparting flame resistance to cellulosic materials wherein said cellulosic material is impregnated with an aqueous monobasic acid solution containing metals selected from the group comprising zirconium, titanium, and antimony, comprises neutralizing at least a portion of the acid present in said impregnated cellulosic material by means of contact with gaseous ammonia. This novel neutralization procedure is continued until at least a substantial portion of the metals has become insolubilized and integrated with the final product.

Ina more specific adaptation of this invention titanium tetrachloride is dissolved in an aqueous medium and antimony trioxide subsequently dissolved in the resulting acidic solution to produce a clear, acidic flame-proofing solution. Cotton fabric is treated by immersion in this solution and the excess liquid removed by squeezing and draining. After allowing a short period of time to elapse during which the chemicals may react with the cellulose, the cloth is then contacted with an atmosphere containing ammonia gas, preferably in a gas tight, or nearly gas tight enclosure. In order to promote good gaseous contact with the interior of the fabric, devices may be used which will cause the ammonia to be drawn or forced through the fabric. When neutralization has been completed the fabric is then waterwashed to remove soluble residues which consist largely of the ammonium salts from the neutralization reaction. There are instances where the complete neutralization by the ammonia gas in one step may not be preferred. For example, in the case of very thick or fragile fabrics the accumulation of ammonium salt crystals may be so great as to mechanically damage the fabric or retard the penetration of the neutralizing gas. In such cases I may neutralize a portion of the acid with gaseous ammonia and then remove the by-product crystals as by washing in water and then proceed to complete the neutralization either by the gaseous ammonia method or by the known methods employing alkaline neutralizing solutions. The advantages of this invention nevertheless are still realized as a result of the first partial gaseous neutralization step. The alkaline solution used may also function to dissolve out the ammonium salt crystals if so desired. Aqueous ammonium hydroxide solution will serve well as such an alkaline solution and its use avoids a multiplicity of alkaline agents.

The use of titanium rather than zirconium in flameproofing compositions is usually preferred for reasons of cost. The composition of the preferred acidic titaniumantimony solution, for example, employed with this invention may vary considerably. The combined Sb2O3-Ti02 content may be anywhere from 25-500 grams per liter, and preferably, in the case of the aqueous solutions, from 200-400 grams per liter. The proportions of titanium and antimony present preferably may range from an atom ratio of antimony to titanium not exceeding 2 and a weight ratio of titanium to antimony ranging up to 10. The aqueous solutions may then be diluted with alcohol or equivalent solvents to obtain certain advantages that are indicated in application Serial #245,089 now U. S. Patent 2,668,784. These solutions may also contain various ancillary agents such as dissolved zinc, tin, borates and the like. Of the monobasic acids which may be used to solubilize the metal content of these solutions, hydrochlonic, formic and acetic or mixtures of them appear to be most satisfactory.

V In one embodiment which uses hydrochloric acid, the aqueous solution contains a total of 200-475 grams per liter of dissolved antimony and titanium calculated as T-iOz and SbzOs. The atom ratio of antimony and titanium in this solution is not more than 2 and the weight ratio of titanium to antimony ranges up to 10. The total chloride content of the solution ranges from 180-500 grams per liter calculated as HCl.

The method of applying the acidic antimony-titanium solution is not critical to this invention, it being only necessary to impregnate or wet the cellulosic material with the acid solution before ammonia neutralization. The ammonia gas neutralization may be applied directly after impregnating the cellulosic material, however, it is usually preferable to carry out various associated operations which are recommended for the application of the particular acidic solution being used. Thus, it is usually desirable to squeeze out or otherwise remove the excess of the solution from the material, the excess referred to being that which is retained in the larger pores and macroscopic interstices of the cellulosic material. Heating or holding for various lengths of time or evaporation of some of the water or of such solvents as alcohol prior to the ammonia gas neutralization may also be practiced.

When the impregnated product is ready for the neutralization step, the ammonia gas may be brought into contact with it by any convenient means. Thus, simple maintenance of the treated material in contact with gaseous ammonia long enough for diffusion of the gas into the material is a satisfactory procedure. However, to speed up the operation or to make the treatment more uniform, especially in the case of thick materials, one may resort to such expedients as forcing the gas through the treated material and subjecting the material to mechanical working such as may be obtained by passing repeatedly through squeeze rolls and over bending or flexing devices. The contact with ammonia gas. may be continued in one stage until the acid residues are thoroughly neutralized or the neutralization may be carried out in incremental steps alternating with auxiliary steps such as washing. In practice the neutralization will usually be carried out according to a predetermined schedule, however, the use of spot tests with pH indicators offers a means of checking the progress of the neutralization.

The process of this invention is found useful in obtaining improved neutralization of acid residues in textile and cellulosic materials. These materials generally include the absorbent organic fibers, fabrics, yarns, etc. of the textile field as well as paper and cellulose derived films of the coating and wrapping fields. Cellophane, for example, while not absorbent in the'same sense as a fabric, nevertheless is swollen by the acidic solutions of this invention to the extent that impregnation will occur. Specific examples of .the substances which will gain resistance to flame, mildew, decay, etc. by. the method of this invention are natural cellulose products such as cotton, linen, ramie, hemp, jute as well as regenerated cellulose products such as rayon, cellophane, and the like, nitrocellulose, cellulose secondary acetate, related hydroxyl containing polymers, and paper. This utility is especially marked in the application of titanium-antimony flameproofing treatments where free acid isessential to maintain these elements in solution as well as to swell the cellulose to admit penetration of the solution. Although the acid is essential, it may not be left in the final product. This ammonia neutralization process is therefore useful in removing these residual acids as well as achieving an improved union of the cellulose and the precipitated metal compounds. 7

A better illustration of some of the practical applications of this invention is furnished by the following examples.

Example I A nine inch circle of a nine ounce olive drab herringbone twill was treated by impregnation with an acidic flame-proofing solution. This solution was prepared in the manner described in U. S. Patent 2,570,566 and contained about 200 g. per liter of TiOz, 200 g. per liter of SbzOs, and 390 g. per liter of HCl. After dipping the cloth was passed through a common hand wash wringer to remove excess of solution. After about 15 minutes the cloth was placed on the perforated plate of a Buchner funnel and covered with an inverted conical glass funnel which fitted inside the Buchner. Ammonia gas from a cylinder connected to the glass funnel stern was forced through the cloth. After two minutes exposure to the gas, during which time the flow was turned on and off several times, the cloth was removed. Spot tests with drops of brorn-phenol blue solution showed no residual free acid present. The cloth was washed and dried to remove the ammonium chloride. No dust or light colored areas were visible on the cloth which was as fully flame-resistant as a similarly treated cloth neutralized in 15% NazCOs solution.

Example II A strip of napped rayon blanket material such as that used in making baby blankets was treated with a flameretarding solution in a standard laboratory padder. The solution used was prepared by diluting 70 parts by weight of a stock solution with 30 parts by weight of 7% aqueous HCl solution. The stock solution contained 160 g./l.

'dissolved TiOz, 290 g./l. dissolved Sb203, 32 g./l. dissolved ZnO, and 460 g./l. HCl with the remainder water. During the padding process the material was immersed and saturated with the solution and then put through a set of squeeze rolls to remove excess. Following this the material was allowed to hang in air at room temperature for 15 minutes to permit reaction between the solution and the rayon. Then ammonia gas neutralization, was carried out in a special cabinet containing gas inlet and outlet, and a set of rubber rolls. The strip of material was placed in the cabinet, threaded into the rolls and lateral guides and the ends sewed to form a continuous belt. The cabinet was then closed, the ammonia gas turned on and the rolls rotated. During the two minute exposure to ammonia the cloth passed through thesqueezing action of the rolls about six times. The ammonia was turned off and the fabric removed and found to retain no residual free acid. After washing and drying the soft fluffy fabric was substantially flash proof and free of dusty residues. 7

Example III A laboratory textile treating range having six dip rolls each followed by a set' of squeeze rolls was adapted for ammonia gas neutralization by enclosing it in a gas-tight cabinet. The seals through which the cloth was fed to and withdrawn from this chamber comprised sets of inflated polyethylene cushions pressing together and between which the fabric could slide. A suitably sized open sided J box was installed ahead of the range and a padder set up to discharge into the J box. A flame-proofing solution containing 60 parts by weight of the stock solution used in Example II per 40 parts of isopropanol was supplied to the padder. Ammonia gas, but no solution, was supplied to the enclosed range after threading in the leader attached to a length of No. 10 black cotton duck. In treating the duck it was passed into the flame-proofing solution, through squeeze rolls on the padder, into the J box through which air was blown. The cloth remained mechanical action of the guide rolls and squeeze rolls in the ammonia atmosphere served to speed the neutralization and make it uniform. The neutralized cloth was then laundered and dried. It was free of dusty discoloration or ghosts which frequently appear on dark colored materials when treated with such flame-proofing solutions by ordinary methods.

Example IV A strip of 6 oz. cotton HBT was impregnated with an acidic flame-proofing solution in a laboratory padder. This solution contained 160 g./l. TiOz, 293 g./l. SbzOs and 460 g./l. HCl. After lagging for minutes one portion of this strip was neutralized by hanging it in a tower containing an excess of NH gas. Another portion of this strip was neutralized by passing it through a laboratory range containing a 15% solution of sodium carbonate. After neutralization both strips were scoured by passing them through the laboratory range. In this instance the first 2 boxes of the range contained a 0.5% solution of a fatty alcohol sodium sulfate detergent available under trade name DuPonol D, and the remaining 5 boxes contained running water. Analyses were made on a sample which was not neutralized and on scoured samples neutralized by the two methods described above. Thus it was found that the cloth picked up on a dry weight basis, 11.7% TiOz and 20.6% SbzOs in passing through the padder. The portion neutralized in soda ash retained 6.7% TiOz and 14.6% SbzOs. The portion neutralized with ammonia retained 11.1% TiOz and 18.6% 811203. From these data it was calculated that the percent retention of flame-proofing solids (TiOa-l-SbzOa) was 91.9% in the case of ammonia neutralization and 65.9% in the case of soda ash neutralization.

It is possible to impregnate fabrics, etc., with any precipitable oxide or hydroxide by this method. Thus, the metals like manganese, chromium, nickel, iron, cobalt, molybdenum, tungsten and the rare earths may be employed when the color of these precipitates is admissible. However, usually in the treatment of such substances the polyvalent metals having water insoluble white or colorless oxides and hydroxides are preferred. These metals are magnesium, zinc, cadmium, aluminum, titanium, zirconium, tin, lead and antimony.

Example III illustrates a substantially continuous method of carrying out this invention. Various other auxiliary devices may be used in applying the ammonia gas. For example, in addition to the mechanical action of the rolls in the range, the cloth may be passed across or around perforated guides while ammonia gas is supplied through the perforations and thus forced through the fabric.

The form of the textile material being treated is not limited to cloth. Thus, cotton or rayon staple may also be treated according to this invention, as well as yarn in skeins, single or multiple strands, etc.

It is usually satisfactory and economical to simply supply pure or concentrated ammonia gas to the neutralizing chamber. One may, however, dilute the ammonia with carrying gas such as air. Dilute ammonia vapor might be desirable in order to avoid generation of too much heat in a delicate or very thick material. Or, in a more complex continuous mechanical device, more efficient use of the ammonia may be realized by using the counter-current principle. In such an adaptation, a gas, e. g. air, will be supplied either initially with the NHs or fed at intermediate points to carry the ammonia residues toward the incoming highly acid material where complete absorption of the NH: is desired.

There appears to be no obvious reason for preferring ammonia to other alkaline neutralizing agents insofar as the chemical reactions are concerned. Previously, aqueous solutions of sodium carbonate, sodium hydroxide and ammonium hydroxide have been used with substantially equal results. However, the physical behavior of the gaseous alkali seems to provide certain advantages.

These advantages are explainable by the theory that the gas dissolves and diffuses into the residual solution in the material with a minimum of liquid displacement. The flame retarding agents therefor remain in the fine structure of the cellulosic while they are neutralized .and fixed. On the other hand, when a fabric impregnated with the first solution is immersed in a second solution there is bound to be some displacement of the first solution either by gross displacement or by diffusion into still acid or neutral liquid phases present just outside the fiber structures. This results in lower eventual oxide content and a dusty deposit in or on the fabric. These undesirable actions are not possible in the case of gaseous neutralization.

The advantages obtained by the novel action of the gaseous ammonia which are realized in practice are quite consistent with the foregoing theory. More efiicient utilization of the titanium, antimony, etc. results because of their substantially complete insolubilization within the fine structure of the fabric. This also accounts for the absence of dust and ghosts which formerly resulted from precipitation after slight displacement by liquid neutralizers. Another advantage pertains to the simplicity of operation, once a suitable enclosure is provided. Specifically, it eliminates making up and handling caustic solutions. Because of the cleaner, less dusty manner in which the metal oxides are fixed within the fibers, vigorous scrubbing to obtain a clean bright product is virtually eliminated. The process of this invention is applicable not only to flame-retarding in textiles and cellulose products such as paper, but also to treatments to improve wet strength and rot and mildew resistance which embody the impregnation of such material with agents precipitable from aqueous acid solutions with alkali.

The improved metal containing cellulosic materim of my invention is substantially free of loosely held precipitated oxides of the metal treating agents as explained above. This means that the said agents are made more highly effective by the gas neutralization of the cellulosic material wetted or impregnated by the acid metal treating reagent. The metal treating reagents are converted to insoluble compounds chemically or physically bonded to the cellulose. The process allows one to obtain more effective use of the metal reagents and at the same time eliminates the deleterious efiects of partially converting the metal reagents to insoluble compounds which are securely bonded to the cellulosic framework. The flameproofness of the treated product is demonstrated by the test currently used in the trade and known as the Vertical Bunsen Burner Test which is described on pages 111-15 of Flameproofing Textile Fabrics, by R. W. Little (1947).

I claim as my invention:

1. A process for rendering cellulosic textile materials resistant to flame which comprises wetting said textile material with an aqueous I-ICl solution containing a total of from 200-475 grams per liter of antimony and titanium in said solution calculated as TiOz and SbzOs, wherein the atom ratio of antimony to titanium is not more than 2 and the weight ratio of titanium to antimony ranges up to 10, and the total chloride content ranging from 500 g./ 1. calculated as HCl, removing excess of said aqueous solution, allowing the treated material to stand until the solution is absorbed within said material, neutralizing the solution within said material with ammonia gas, washing the treated material and recovering an improved flame-resistant product.

2 In a process for improving Water-insoluble, free hydroxyl-containing cellulosic material selected from the group consisting of paper, textiles, and films which comprises penetrating said material with an aqueous acidic solution of antimony and a metal selected from the group consisting of titanium and zirconium, said solution containing 25-500 grams per liter of the antimony and said metal calculated as SbaOs, TiOz and ZrOz, and the atomic ratio 7 of antimony to said metal is not greater than 2, the improvement which comprises neutralizing the solution in the treated material with ammonia gas and recovering a flameresistant product.

3. In a process for improving water-insoluble, free hydroxyl-containing cellulosic material selected from the group consisting of paper, textiles, and films which comprises penetrating said material with an aqueous acidic solution of antimony and a metal selected from the group consisting of titanium and zirconium, said solution containing 25-500 grams per liter of the antimony and said metal calculated as SbzOs, TiO2 and ZrO2, and the atomic ratio of antimony to said metal is not greater than 2, the improvement which comprises partially neutralizing the solution in the treated material with ammonia gas, Washing the partially neutralized material and then completely neutralizing the remaining acid solution in the treated material with an alkaline agent;

4. In a process for modifying water-insoluble, free hydroxyl-containing cellulosic material selected from the group consisting of paper, textiles, and films which comprises Wetting said material with an alcoholic aqueous acidic solution of antimony and a metal selected from the group consisting of titanium and zirconium, said solution containing 25-500 grams per liter of the antimony and said metal calculated as SbzOs, TiO2 and ZrOz and the atomic ratio of antimony to said metal is not greater than 2, the improvement which comprises evaporating a portion of the alcohol from the wetted cellulosic material and then neutralizing the solution in the treated material with ammonia gas.

5. In a process for improving water-insoluble, free prises penetrating said material with an aqueous acidic solution of antimony and a metal selected from the group containing titanium and zirconium, said solution containing 25-500 grams per liter of antimony and said metal calculated as SbzOs, TiO2 and ZrOz, the atomic ratio of antimony to said metal is not greater than 2, the improvement which comprises simultaneously mechanically working'said material and neutralizing the acidic solution in said material with ammonia gas and recovering a flame-resistant product.

6. In a process for improving water-insoluble, free hydroXyl-containing cellulosic material selected from the group consisting of paper, textiles, and films which cornprises penetrating said material with an aqueous acidic V solution containing dissolved antimony trioxide and a titanium tetrachloride, said solution containing 25-500 hydroxyl-containing cellulosic material selected from the group consisting of paper, textiles, and films which corngrams per liter of antimony and titanium calculated as SbzOs and TiO2 and the atomic ratio-of antimony to titanium metal is not greater than 2, the improvement which comprises neutralizing the solution in the treated material with ammonia gas and recovering a flameresistant product.

References Cited in the file of this patent UNITED STATES PATENTS 1,717,483 White June 18, 1929 2,306,222 Patnode Dec. 22, 1942 2,607,729 Dills Aug. 19, 1952 2,668,784 Dills Feb. 9, 1954 OTHER REFERENCES Industrial and Engineering Chemistry, March 1950, pp. 440-444. 

2. IN A PROCESS FOR IMPROVING WATER-INSOLUBLE, FREE HYDROXYL-CONTAINING CELLULOSIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF PAPER, TEXTILES, AND FILMS WHICH COMPRISES PENETRATING SAID MATERIAL WITH AN AQUEOUS ACIDIC SOLUTION OF ANTIMONY AND A METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM, SAID SOLUTION CONTAINING 25-500 GRAMS PER LITER OF THE ANTIMONY AND SAID METAL CALCULATED AT SB2O3, TIO2 AND ZRO2, AND THE ATOMIC RATIO OF ANTIMONY TO SAID METAL IS NOT GREATER THAN 2, THE IMPROVEMENT WHICH COMPRISES NEUTRALIZING THE SOLUTION IN THE TREATED MATERIAL WITH AMMONIA GAS AND RECOVERING A FLAMERESISTANT PRODUCT. 